netdev - Re: [PATCH RFC 2/2] net: qualcomm: new Ethernet over SPI driver for QCA7000

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Message-ID: <4860368.6Apskanc4s@wuerfel>
Date:	Tue, 29 Apr 2014 10:14:08 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Stefan Wahren <stefan.wahren@...e.com>
Cc:	davem@...emloft.net, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, f.fainelli@...il.com, netdev@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH RFC 2/2] net: qualcomm: new Ethernet over SPI driver for QCA7000

On Tuesday 29 April 2014 08:51:26 Stefan Wahren wrote:
> Am 28.04.2014 22:09, schrieb Arnd Bergmann:
> > On Monday 28 April 2014 19:54:57 Stefan Wahren wrote:
> >> +/*   Dumps the contents of all SPI slave registers.        */
> >> +static int
> >> +qcaspi_regs_dump(struct seq_file *s, void *what)
> >> +{
> >> +    struct reg {
> >> +            char *name;
> >> +            u32 address;
> >> +    };
> >> +
> >> +    static struct reg regs[] = {
> >> +            { "SPI_REG_BFR_SIZE", SPI_REG_BFR_SIZE },
> >> +            { "SPI_REG_WRBUF_SPC_AVA", SPI_REG_WRBUF_SPC_AVA },
> >> +            { "SPI_REG_RDBUF_BYTE_AVA", SPI_REG_RDBUF_BYTE_AVA },
> >> +            { "SPI_REG_SPI_CONFIG", SPI_REG_SPI_CONFIG },
> >> +            { "SPI_REG_SPI_STATUS", SPI_REG_SPI_STATUS },
> >> +            { "SPI_REG_INTR_CAUSE", SPI_REG_INTR_CAUSE },
> >> +            { "SPI_REG_INTR_ENABLE", SPI_REG_INTR_ENABLE },
> >> +            { "SPI_REG_RDBUF_WATERMARK", SPI_REG_RDBUF_WATERMARK },
> >> +            { "SPI_REG_WRBUF_WATERMARK", SPI_REG_WRBUF_WATERMARK },
> >> +            { "SPI_REG_SIGNATURE", SPI_REG_SIGNATURE },
> >> +            { "SPI_REG_ACTION_CTRL", SPI_REG_ACTION_CTRL }
> >> +    };
> >> +
> >> +    struct qcaspi *qca = s->private;
> >> +    int i;
> >> +
> >> +    for (i = 0; i < (sizeof(regs) / sizeof(struct reg)); i++) {
> >> +            u16 value;
> >> +
> >> +            qcaspi_read_register(qca, regs[i].address, &value);
> >> +            seq_printf(s, "%-25s(0x%04x): 0x%04x\n",
> >> +                    regs[i].name, regs[i].address, value);
> >> +    }
> >> +
> >> +    return 0;
> >> +}
> > Shouldn't these just come through ethtool --register-dump ?
> 
> yes, that's right. But from my point of view this have 2 disadvantages:
> 
> - the interface to ethtool needs to be maintained (i'm not sure if i
> have all debug information)
> - the target platform needs ethtool

i think it's more important to use standard interfaces here. A random
user trying to debug a problem with this hardware may know about ethtool
or find that documented somewhere, but wouldn't know about the debugfs
interfaces without reading the driver source code.

The ethtool interface is also easier to maintain than the debugfs
files.

> >> +static irqreturn_t
> >> +qcaspi_intr_handler(int irq, void *data)
> >> +{
> >> +    struct qcaspi *qca = (struct qcaspi *) data;
> >> +    qca->intr_req++;
> >> +    if (qca->spi_thread &&
> >> +            qca->spi_thread->state != TASK_RUNNING)
> >> +            wake_up_process(qca->spi_thread);
> >> +
> >> +    return IRQ_HANDLED;
> >> +}
> > What is the advantage of using your own thread mechanism for receiving
> > data instead of the normal NAPI method?
> 
> This mechanism comes from Qualcomm and was originally designed for
> Kernel 2.6.35. I never
> talked to them.  Currently i don't know how to port this driver to NAPI.
> It sounds to me, that's a lot of work and i need more knowledge.

As far as I know it's also not mandatory.

If the hardware interfaces require calling sleeping functions, it
may not actually be possible, but if you can use it, it normally
provides better performance.

> Is there a porting guide for NAPI?

Google points me to
http://www.linuxfoundation.org/collaborate/workgroups/networking/napi

> Does this mean the current state of the driver should better go to staging?

Probably not, the driver doesn't look bad overall.

	Arnd
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